<head>
    <title>demo4</title>
    <meta http-equiv="Content-Type" content="text/html;charset=UTF-8">
    <script src="https://cdn.jsdelivr.net/npm/vue@2.6.10/dist/vue.js"></script>
  </head>
  <body>
    <div id="app">
      <button-counter></button-counter>
    </div>
  </body>